arm64: Use the reserved TTBR0 if context switching to the init_mm

The idle_task_exit() function may call switch_mm() with next == &init_mm. On arm64, init_mm.pgd cannot be used for user mappings, so this patch simply sets the reserved TTBR0. Cc: <[email protected]> Reported-by: Jon Medhurst (Tixy) <[email protected]> Tested-by: Jon Medhurst (Tixy) <[email protected]> Signed-off-by: Catalin Marinas <[email protected]>
mrcsosa · Mar 23, 2015 · e53f21b · e53f21b
1 parent bc465aa
commit e53f21b
Showing 1 changed file with 9 additions and 0 deletions.
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
@@ -151,6 +151,15 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 {
 	unsigned int cpu = smp_processor_id();
 
+	/*
+	 * init_mm.pgd does not contain any user mappings and it is always
+	 * active for kernel addresses in TTBR1. Just set the reserved TTBR0.
+	 */
+	if (next == &init_mm) {
+		cpu_set_reserved_ttbr0();
+		return;
+	}
+
 	if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next)
 		check_and_switch_context(next, tsk);
 }